use admin to redact if the user isn't ours

synapse/handlers/admin.py

@@ -73,6 +73,8 @@ def __init__(self, hs: "HomeServer"):
             self._redact_all_events, REDACT_ALL_EVENTS_ACTION_NAME
         )
 
+        self.hs = hs
+
     async def get_redact_task(self, redact_id: str) -> Optional[ScheduledTask]:
         """Get the current status of an active redaction process
 
@@ -423,8 +425,10 @@ async def _redact_all_events(
         user_id = task.params.get("user_id")
         assert user_id is not None
 
+        # puppet the user if they're ours, otherwise use admin to redact
         requester = create_requester(
-            user_id, authenticated_entity=admin.user.to_string()
+            user_id if self.hs.is_mine_id(user_id) else admin.user.to_string(),
+            authenticated_entity=admin.user.to_string(),
         )
 
         reason = task.params.get("reason")